This invention relates to a one-way clutch of simple construction and low cost for which no high precision is required.
As for example disclosed in Japanese Unexamined Patent Publication No. 2869062, there is known a simple one-way clutch for low torque transmission in which is applied the principle of a two-shaft belt power transmission mechanism for transmitting torque between two shafts by way of a belt looped therebetween.
This clutch includes a first rotation member of flat pulley shape that is coupled to either one of the drive and driven sides, and a second rotation member that is assembled rotatably with the first rotation member and coupled to the other of the drive and driven sides. Radially outside of the first rotation member is disposed a shaft member which is in parallel with the rotation axis of both the rotation members, and both ends of the shaft member are pressed into corresponding shaft bores provided in the second rotation member, respectively. A rocking member of substantially arcuate cross section is supported for rocking motion on the shaft member. A belt is looped between the outer periphery of the rocking member and the outer periphery of the first rotation member so that it creates two spans therebetween. On the other hand, attached to the second rotation member is a biasing means for tending to radially inwardly press one end of the rocking member in a circumferential direction thereof, whereby the other end of the rocking member in the circumferential direction radially outwardly presses one span of the belt to place an initial tension on the belt.
When torque is input to the clutch in a direction to relatively rotate both the rotation members such that the span pressed by the biasing means will provide a slack-side span, the belt tension is maintained or increased and therefore the torque is transmitted between the first and second rotation members via the belt. In contrast, when torque is input to the clutch in a direction to relatively rotate both the rotation members such that the span pressed by the biasing means will provide a tight-side span, the belt tension is reduced so that the belt slips on at least one of the outer peripheries of both the rocking member and the first rotation member, which blocks torque transmission.
While a typical conventional one-way clutch is a precision machinery component in which a plurality of intermediate members are arranged for establishing and blocking torque transmission between inner and outer rings and a spring member is provided for urging each of the intermediate members in a direction to allow for torque transmission, the belt-type one-way clutch as described above needs no highly precise parts and has a simplified construction. Therefore, the belt-type one-way clutch has the advantage of being manufactured at low cost.
Further, when excessively large torque is input to the clutch, the belt can be broken to block further torque transmission. This also offers the advantage of low cost in that there is no need for the clutch to additionally include a torque limiter. In addition, the belt-type one-way clutch is also economically advantageous in that even if the belt has been broken, the clutch can be used again by replacing the broken belt with new one.
Meanwhile, since the belt-type one-way clutch originally has a simpler construction as compared with the typical one-way clutch, it can only necessarily transmit relatively small torque. In terms of its use, however, there is a strong demand for such a clutch that transmits as large torque as possible even if it is for low torque transmission.
In order to increase the magnitude of transmittable torque of the belt-type one-way clutch, the following several measures have been required:
1) to enhance the tensile strength of the belt;
2) to enhance the strength of the rocking member receiving pressure due to a belt tension with a smaller area than the first rotation member; and
3) to enhance the strength of the shaft member which supports the rocking member thereon.
Further, as a user side demand, weight reduction is also strongly needed in addition to rise in transmittable torque magnitude. In this respect, making the second rotation member from aluminum alloy has yet been taken as a measure.
Problem to be Solved
However, the above-described one-way clutch has a problem in that load placed on the shaft member is concentrated at the shaft bores of the second rotation member in which both ends of the shaft member are held so that excessively large stress will be produced at the shaft bores.
In particular, if the second rotation member is made from aluminum alloy for weight reduction, the problem resulting from excessively large stress will outstandingly appear.
In view of the foregoing problem, a primary object of the present invention is to provide a belt-type one-way clutch which applies the principle of a two-shaft belt power transmission mechanism and which can increase the magnitude of transmittable torque while avoiding constraints placed due to the use of aluminum alloy as material of the second rotation member for its weight reduction by suppressing stress produced due to load of the shaft member being concentrated at shaft bores of the second rotation member which held respective ends of the shaft member in order to increase the magnitude of transmittable torque.
To solve the foregoing problem, the present invention takes the following solutions.
A first solution of the invention is a one-way clutch comprising: a first rotation member that has a working surface of circular cross section formed in an outer periphery thereof and is coupled to one of drive and driven sides; a second rotation member that is assembled with the first rotation member so as to rotate around the central axis of the working surface of the first rotation member and is coupled to the other of the drive and driven sides; a shaft member that is disposed radially outside of the working surface of the first rotation member to extend in parallel with the central axis of the working surface and is held at both ends thereof by the second rotation member; a rocking member that is placed radially outside of the working surface of the first rotation member, has a working surface of arcuate cross section formed in an outer periphery thereof and is supported for rocking motion on the shaft member; a friction member that is looped between both the working surfaces of the first rotation member and the rocking member to create two spans between the first rotation member and the rocking member; and a biasing member for tending to rotate the rocking member around the axis of the shaft member so that the rocking member presses one of the spans of the friction member, wherein both the ends of the shaft member are held by the second rotation member through respective support members that each cover side and end surfaces or at least the side surface of the corresponding end of the shaft member.
According to this solution, when the tension of the friction member is increased due to torque input to the one-way clutch, the load placed on the rocking member will be correspondingly increased and concentrated at holding portions of the second rotation member which hold both the ends of the shaft member. In this case, each of the support members, which is interposed between the corresponding end of the shaft member and the corresponding holding portion of the second rotation member, disperses the load so that stress produced within the holding portion of the second rotation member due to the load concentration can be suppressed to a low level. This avoids the situation that the stress as described above deforms the holding portion of the second rotation member to involve a mal-operation of the one-way clutch.
A second solution of the invention is based on the first solution, wherein the second rotation member is made from aluminum alloy. According to this solution, the second rotation member made from aluminum alloy can be reduced in weight as compared with the conventional second rotation member made from steel for example. Further, in the case of using the second rotation member made from aluminum alloy poorer in strength than the steel-made one, the support members can particularly effectively obviate deformation of the holding portion of the second rotation member.
A third solution of the invention is based on the first solution, wherein the second rotation member has shaft bores for respectively holding both the ends of the shaft member, and the support members are pressed into the respective shaft bores. Further, a fourth solution of the invention is based on the first solution, wherein the second rotation member is made by die casting, and the support members are insert molded in the second rotation member. In these manners, the effects of the first solution can be specifically implemented.
A fifth solution of the invention is based on the fourth solution, wherein the second rotation member is formed of a first half placed on one side in an axial direction with respect to an imaginary plane which is in the middle of the shaft member and orthogonal to the shaft member, and a second half placed on the other side in the axial direction with respect to the imaginary plane and molded using the same die as used for the first half.
According to this solution, the second rotation member is constituted by two halves bonded in its axial direction and the two halves are molded using the same die. Therefore, the cost for molding of the second rotation member can be reduced as compared with the case of using different dies to mold two halves.
A sixth solution of the invention is based on the first solution, wherein the rocking member is made by forging. In this manner, the forged rocking member has higher strength than that of other rocking members made by casting for example, which contributes to transmission of larger torque of the one-way clutch and enhances durability thereof.
A seventh solution of the invention is based on the first solution, wherein the working surface of the first rotation member is machined.
According to this solution, since machining treatment is applied to the working surface of the first rotation member, the frictional force developed between the first rotation member and the friction member can be suppressed to a low level. This provides smooth sliding between the working surface of the first rotation member and the friction member and suppresses abrasion of the friction member by a reduction of the frictional force.
Effects of the Invention
In the first solution of the present invention, the one-way clutch is arranged so that the second rotation member is rotatably assembled with the first rotation member, the friction member is looped between the working surface of the rocking member supported for rocking motion by the shaft member held at both ends by the second rotation member and the working surface of the first rotation member, and the rocking member biased by the biasing member presses one span of the friction member to place an initial tension on the friction member, wherein both the ends of the shaft member are held by the second rotation member through the support members that each cover at least the side surface of the corresponding end of the shaft member. Therefore, load of the shaft member which would be concentrated at the holding portions of the second rotation member which hold both the ends of the shaft member is dispersed so that stress produced within the holding portions can be suppressed to a low level. This increases the magnitude of transmittable torque while avoiding constraints placed on the one-way clutch by reducing the weight of the second rotation member through replacement of material used.
According to the second solution of the invention, since the second rotation member is made from aluminum alloy, the second rotation member can be reduced in weight and concurrently the effects of the first solution can be obtained to a full extent.
According to the third solution of the invention, when the second rotation member has shaft bores for respectively holding both the ends of the shaft member, the support members as described above are pressed into the shaft bores, respectively. Therefore, the effects of the first solution can properly be obtained.
According to the fourth solution of the invention, when the second rotation member is made by die casting, the support members are insert molded in the second rotation member. Therefore, the same effects as exhibited by the third solution can be obtained.
According to the fifth solution of the invention, since the second rotation member is formed of a first half placed on one side with respect to its axial direction and a second half which is placed on the other side and molded using the same die as used for the first half, i.e., these two halves are formed using the same die, the cost for molding of the second rotation member can be reduced.
According to the sixth solution of the invention, since the rocking member is made by forging, its strength can be enhanced, which contributes to transmission of larger torque and enhancement in durability of the one-way clutch.
According to the seventh solution of the invention, since the working surface of the first rotation member is machined, the frictional force between the working surface of the first rotation member and the friction member can be reduced. This provides smooth blockage of torque transmission due to slide between the working surface of the first rotation member and the friction member and suppresses abrasion of the friction member that may be induced by such slide.